If your server doesn't have a GUI, you'll have to edit your ~/.TRIGGERcmdData/commands.json file manually, using a text editor like vi (aka vim) or pico, nano etc.

On Linux, your default ~/.TRIGGERcmdData/commands.json file includes the first 5 commands. I added the 6th command you could use to restart mysql, like Google says.

[
  {"trigger":"Reboot","command":"shutdown -r","ground":"background","voice":"reboot","allowParams": "false"},
  {"trigger":"Gnome Editor","command":"gedit","ground":"foreground","voice":"notepad","allowParams": "false"},
  {"trigger":"Calculator","command":"gnome-calculator","ground":"foreground","voice":"calculator","allowParams": "false"},
  {"trigger":"yum update","command":"yum -y update","ground":"background","voice":"yum update","allowParams": "false"},
  {"trigger":"apt update","command":"apt-get -y update","ground":"background","voice":"update","allowParams": "false"},
  {
    "trigger": "Restart MySQL",
    "command": "sudo systemctl restart mysql",
    "offCommand": "",
    "ground": "background",
    "voice": "restart",
    "voiceReply": "",
    "allowParams": "false"
  }
]

Notice I made "ground" = "background" because without a GUI, you probably installed the background agent (with installdaemon.sh) which runs the TRIGGERcmd agent in background mode as service.